In recent years, vehicle trajectory control is commonly performed for an automation of a steering angle control, which may be based on, for example, a motor rotation angle, a steering rotation angle, a yaw rate sensor, a deviation between a tire steer angle and its target value, a lateral shift of position from a target position derived from a camera, a laser radar, a millimeter wave radar, etc., a deviation from a target trajectory based on GPS information and the like, and a deviation relative to a curvature obtained from a road geometry.
Further, a lane keeping control in which a relationship between a currently-traveling lane and a subject vehicle is detected based on image information from the camera that captures a front field image of the subject vehicle and a suitable steering angle is provided for an along-the-lane travel of the vehicle is also common, and a power steering control (i.e., an assist control) for assisting a steering operation by a driver, both of which may already be realized by an apparatus that uses only one actuator (e.g., a motor), as disclosed in a patent document 1, JP H9-221053 A.
Fundamentally, in such apparatus, the motor is driven based on a sum between a required torque for the assist control and a required torque for the vehicle trajectory control. However, during the vehicle trajectory control, the required torque for the assist control is multiplied by a suppression factor having a value between 0 and 1, which somewhat reduces the influence of the assist control, to keep the trajectory from departing the currently-traveling lane.
In the above-described situation, when an intervention operation by the driver (i.e., Driver Override (DOR) is performed during the vehicle trajectory control, the deviation of the actual position and the actual angle from the target position and the target angle increases. Then, in the vehicle trajectory control, a cancelling torque for cancelling an increased deviation between the target position/angle and the actual position/angle is generated, which may interfere with the driver's operation. This leaves a wrong steering feel for the driver. To reduce such a wrong steering feel, the responsiveness of the vehicle trajectory control must be lowered. However, when the responsiveness of the vehicle trajectory control is simply lowered, the original functionality of the vehicle trajectory control may also deteriorate.
Further, under a certain circumstance, the vehicle trajectory control must be prioritized over the intervention operation by the driver, depending on a degree of urgency and/or a degree of necessity of the circumstance, (e.g., to avoid collision or the like). In other words, the vehicle trajectory control may override the assist control depending on a situation. However, a balance between the two demands (i.e., between (i) an urgency avoidance, that is, a control by a system intervention/override and (ii) a switching of controls without providing a wrong steering feeling) has been very difficult to achieve so far (i.e., as trade-off matters).